| Replacement of insulin-secreting beta cells by islet transplantation has the potential to restore physiological blood glucose homeostasis. Currently, human cadaveric organ donors are the only source of islets, however, alternative sources such as xenogeneic islets are being investigated. We have established a method for the large scale isolation of islets from neonatal pigs which are glucose responsive and can reverse hyperglycemia in small and large animal models of diabetes.; Islets from neonatal pigs are comprised of a heterogeneous mixture of hormone-producing cells and undifferentiated precursors, which can differentiate, survive and function after transplantation. The objectives of this thesis are two-fold: (1) Examine the differentiation potential of these precursor cells and (2) Assess the survival and functional capabilities of beta cells after exposure to high glucose or diabetogenic cytotoxins. The aim of these studies is to indirectly demonstrate that neonatal porcine islets are advantageous for clinical use over adult islets according to the objectives outlined in this thesis.; Precursor cell differentiation was examined after adenoviral mediated over-expression of the transcription factor neurogenin 3. In infected cells, the fraction of glucagon-positive cells was significantly increased. Partial beta cell differentiation was achieved by incubation of islets in high glucose culture media (28.0 mmol/l).; Survival and function after chronic exposure to high glucose or brief exposure to the diabetogenic cytotoxin, streptozotocin was also examined. A 7 day culture period in 28.0 mmol/l glucose, failed to irreversibly impair glucose responsiveness, or cause a significant increase in beta cell death. Susceptibility to streptozotocin was demonstrated in vitro by significantly reduced islet secretory activity and in vivo by elevated transplant recipient blood glucose levels. In contrast, graft beta cells which differentiated from precursors exposed to hyperglycemia after transplantation into diabetic mice developed streptozotocin resistance.; In summary, islets from neonatal porcine pancreases contain many precursor cells that can be induced to differentiate into endocrine cells with the ability to survive and function after exposure to high glucose and diabetogenic cytotoxins. These advantageous characteristics of neonatal porcine islets may result in better long-term function and protection from cytokine or free radical induced damage after xenotransplantation. |
